Chapter 10
Anatomy of the Muscular System
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 1
Introduction
(Figures 10-5 and 10-6)

There are more than 600 skeletal muscles
in the body

From 40% to 50% of body weight is skeletal
muscle

Muscles, along with the skeleton, determine
the form and contour of the body
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 2
Skeletal Muscle Structure
(Figure 10-1)

Connective tissue components

Endomysium—delicate connective tissue
membrane that covers specialized skeletal
muscle fibers

Perimysium—tough connective tissue binding
together fascicles

Epimysium—coarse sheath covering the muscle
as a whole

These three fibrous components may become
a tendon or an aponeurosis
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 3
Skeletal Muscle Structure

Size, shape, and fiber arrangement (Figure 10-2)

Skeletal muscles vary considerably in size, shape, and fiber
arrangement

Size—range from extremely small to large masses

Shape—variety of shapes such as broad, narrow, long,
tapering, short, blunt, triangular, quadrilateral, irregular, flat
sheets, or bulky masses

Arrangement—variety of arrangements such as parallel to
long axis, converge to a narrow attachment, oblique,
pennate, bipennate, or curved; the direction of fibers is
significant because of its relationship to function
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 4
Skeletal Muscle Structure

Attachment of muscles (Figure 10-3)

Origin—point of attachment that does not move
when muscle contracts

Insertion—point of attachment that moves when
muscle contracts
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 5
Skeletal Muscle Structure

Muscle actions

Most movements are produced by the coordinated action of
several muscles; some muscles in the group contract while
others relax
• Prime movers (agonists)—muscles or groups of muscles that
directly perform a specific movement
• Antagonists—muscles that, when contracting, directly oppose
prime movers; relax while prime movers (agonists) are
contracting to produce movement; provide precision and control
during contraction of prime movers
• Synergists—muscles that contract at the same time as the
prime movers; they facilitate prime movers’ actions to produce
a more efficient movement
• Fixator muscles—joint stabilizers
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 6
Skeletal Muscle Structure

Lever systems

In the human body, bones serve as levers and joints
serve as fulcrums; contracting muscle applies a pulling
force on a bone lever at the point of the muscle’s
attachment to the bone, causing the insertion bone to
move about its joint-fulcrum

Lever system—composed of four component parts
(Figure 10-4):
• Rigid bar (bone)
• Fulcrum (F) around which the rod moves (joint)
• Load (L) that is moved
• Pull (P) that produces movement (muscle contraction)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 7
Skeletal Muscle Structure

Lever systems (cont.)


First-class levers
• Fulcrum lies between the pull and the load
• Not abundant in human body; serve as levers of stability
Second-class levers
• Load lies between the fulcrum and the joint at which pull
•
•
•
•
•
is exerted
Controversy exists regarding presence of these levers
in the human body
Third-class levers
Pull is exerted between the fulcrum and the load
Permit rapid and extensive movement
Most common type of lever found in the body
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 8
How Muscles Are Named

Muscle names can be in Latin or English
(this book uses English)

Muscles are named using one or more of the
following features:


Location, function, or shape (Tables 10-1; 10-2; 10-3)

Direction of fibers—named according to fiber orientation
(Table 10-4)

Number of heads or divisions (Table 10-4)

Points of attachment—origin and insertion points

Relative size—small, medium, or large (Table 10-5)
Names supply hints on how to deduce muscle actions
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 9
Important Skeletal Muscles

Muscles of facial expression—unique in that at
least one point of attachment is to the deep
layers of the skin over the face or neck
(Figures 10-7 and 10-8; Table 10-6)

Muscles of mastication—responsible for chewing
movements (Figure 10-9; Table 10-6)

Muscles that move the head—paired muscles on
either side of the neck are responsible for head
movements (Figure 10-10; Table 10-7)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 10
Trunk Muscles

Muscles of the thorax—critical importance in
respiration (Figure 10-9; Table 10-8)

Muscles of the abdominal wall—arranged in three
layers, with fibers in each layer running in different
directions to increase strength
(Figure 10-12; Table 10-9)

Muscles of the back—bend or stabilize the back
(Figure 10-13; Table 10-10)

Muscles of the pelvic floor—support the structures in
the pelvic cavity (Figure 10-14; Table 10-11)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 11
Upper Limb Muscles

Muscles acting on the shoulder girdle—muscles
that attach the upper extremity to the torso are
located anteriorly (chest) or posteriorly (back and
neck); these muscles also allow extensive
movement (Figure 10-15; Table 10-12)

Muscles that move the upper arm—the shoulder
is a synovial joint allowing extensive movement in
every plane of motion (Figure 10-17; Table 10-13)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 12
Upper Limb Muscles

Muscles that move the forearm—found proximally
to the elbow and attach to the ulna and radius
(Figures 10-19 and 10-20; Table 10-14)

Muscles that move the wrist, hand, and fingers—
these muscles are located on the anterior or
posterior surfaces of the forearm
(Figures 10-21 through 10-23; Table 10-15)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 13
Lower Limb Muscles

The pelvic girdle and lower extremity function in
locomotion and maintenance of stability

Muscles that move the thigh and lower leg
(Figures 10-5, 10-6, and 10-24 through 10-30;
Tables 10-16 and 10-17)
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 14
Lower Limb Muscles

Muscles that move the ankle and foot
(Figures 10-31 and 10-32; Table 10-18)

Extrinsic foot muscles are located in the leg and
exert their actions by pulling on tendons that insert
on bones in the ankle and foot; responsible for
dorsiflexion, plantar flexion, inversion, and eversion

Intrinsic foot muscles are located within the foot;
responsible for flexion, extension, abduction, and
adduction of the toes
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 15
Posture


Maintaining the posture of the body is one of
the major roles muscles play
“Good posture”—body alignment that most
favors function and requires the least
muscular work to maintain, keeping the
body’s center of gravity over its base
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 16
Posture

How posture is maintained

Muscles exert a continual pull on bones in the
opposite direction from gravity

Structures and systems other than muscle and
bones have a role in maintaining posture
• Nervous system—responsible for determining muscle
tone and also regulation and coordination of the amount
of pull exerted by individual muscles
• Respiratory, digestive, excretory, and endocrine systems
all contribute to maintain posture
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 17
Cycle of Life: Muscular System

Muscle cells—increase or decrease in
number, size, and ability to shorten at
different periods

Pathological conditions at different periods
may affect the muscular system
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 18
Cycle of Life: Muscular System

Life cycle changes—manifested in other
components of functional unit


Infancy and childhood—coordination and
controlling of muscle contraction permits
sequential development steps
Degenerative changes of advancing age
result in replacement of muscle cells with
nonfunctional connective tissue

Diminished strength
Mosby items and derived items © 2007, 2003 by Mosby, Inc.
Slide 19